The charge slip includes a tip line you see as inappropriate? Fill it in with a zero, problem solved.

A long and passionate thread about tipping in the Dining Buzz forum was recently shut down, shortly before this interesting article appeared in the NY Times.

Tip, or don't tip. But why inconvenience yourself because of a computer program? I don't order through services that charge an automatic delivery charge--around here I can still phone and order directly from the restaurant, leaving me a choice. And I'll tip the driver/delivery person in cash rather than add to the charge amount.